support PHP yar protocol

[qdaxb]

Yar is a widely used php rpc framework. We could implement the protocol of yar to support cross-language invocation.

There might be three steps:

• Support yar protocol for Motan server, then a php yar client could call java services
• Support yar protocol for Motan client. It might be a little harder because of we need to support short connection on Motan client side.
• Support long connection on php side to improve performance, maybe http/2 is a good option.

[ghost]

this function is what i am looking for! very very great ! exciting!

[chaneychan]

cool，We are waiting for this feature.

[rayzhang0603]

yar protocol will supporting soon！you can try it in here https://github.com/weibocom/motan/tree/feature/yar
please let me know if you have any problems.

[qdaxb]

done
#160